#ifndef __Sales_data_H
#define __Sales_data_H
#include <string>
struct Sales_data{
	std::string isbn() const {return bookNo;}
	Sales_data & combine(const Sales_data &);
	double avg_price() const;
	std::string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;
};
Sales_data add(const Sales_data &, const Sales_data &);
std::ostream & print(std::ostream &, const Sales_data &);
std::istream & read(std::istream &, Sales_data &);
#endif
